Electrochemical grinding methods and apparatus

ABSTRACT

A device for electrochemical grinding by removing material from the surface of a conducting workpiece, comprising a conformator tool including two separate members, a first member for a quick attack of a rough shaped workpiece, comprising a support, one front-end of which is shaped as the compliment of the sectional contour to be obtained along the outer periphery of the workpiece, which operates during a first step of the operation; a high electrolyte flow output supply; a high density current electricity source; and the second member is an electrolytic grinder operating at the rear part of the support, for grinding the workpiece to the desired final shape, the rear part of the support constituting a damming bulk for the electrolyte.

p 10, 1974 H. M. BOURDIOLYLE ETAL 3,835,016-

ELECTROCHEMICAL GRINDING METHODS AND APPARATUS 2 Sheets-Sheet 1 FiledJuly 5. 197,?

p 10, 1974 H. M. BOURIIJYOLLE AL 3,835,016-

ELECTROCHEMICAL GRINDING METHODS AND APPARATUS Filed July 5 1972 2Sheets-Sheet 2 United States Patent 3,835,016 ELECTROCHEMICAL GRINDINGMETHODS AND APPARATUS Henri M. Bourdolle, Serge R. Lacroix, Jean E.Fleury,

Gilbert Peuillot, and Jean Pinot, Billancourt, France,

assignors to Regie Nationale des Usines Renault, Billancourt, andAutomobiles Peugeot, Paris, France Filed July 5, 1972, Ser. No. 269,076

Claims priority, application France, July 26, 1971,

7127282 Int. Cl. B23p 1/02, 1/10, 1/12 US. Cl. 204-224 M 5 ClaimsABSTRACT OF THE DISCLOSURE A device for electrochemical grinding byremoving material from the surface of a conducting workpiece, comprisinga conformator tool including two separate members, a first member for aquick attack of a rough shaped workpiece, comprising a support, onefront-end of which is shaped as the compliment of the sectional contourto be obtained along the outer periphery of the workpiece, whichoperates during a first step of the operation; a high electrolyte flowoutput supply; a highdensity current electricity source; and the secondmember is an electrolytic grinder operating at the rear part of thesupport, for grinding the workpiece to the desired final shape, the rearpart of the support constituting a damming bulk for the electrolyte.

The present invention relates in general to electrochemical grindingmethods and apparatus, and has specific reference to improvementsbrought to these methods and apparatus with a view to increaseconsiderably the rate of shaping of the workpiece to be treated whilereducing appreciably the cost of the device for a given degree ofprecision of the operation.

Electrolytic grinding devices are already known Wherein a drivingdiamond grinding wheel receiving a negative charge and consisting ofsintered copper is pressed against the workpiece connected to thepositive terminal of a generator.

However, during this process a problem must be solved; this problem liesin the simultaneous presence of two contributing effects. In fact, thegreater the contact surface area and the shorter the distance betweenthe grinding wheel and the workpiece, the faster the electrolyticmachining operation, since these conditions promote the passage ofcurrent and therefore the erosion of the anode-forming workpiece.

Thus, in said electrochemical process during the initial contact betweena grinding wheel and a circular workpiece, only very moderate areastangent to the two members involved are actually operative; thus, theelectric exchange or transfer is rather limited, and therefore theattack is relatively moderate.

In contrast thereto, when the tool has penetrated more deeply into theworkpiece, so that the latters surface has assumed a shape complimentaryto the wheel shape, the greater surface areas in mutual contact promotea stronger electrical exchange, thus producing a faster grinding action.

However, another factor becomes elfective concurrently with theabove-defined one:

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The rapidity of the attack is also proportional to the electrolyteoutput at the interface formed between the grinding wheel and theworkpiece; now, this electrolyte output will always be greater duringthe initial period of the machining operation, when nothing prevents itsflow between the workpiece and the grinding wheel.

On the contrary, during the operation, i.e. when the tool has worked itsway into the workpiece material, the electrolyte undergoes a loss ofpressure due to the restricted flow passage so that its output isimpaired.

Moreover, considering the fact that in the case of electrochemicalgrinding it is necessary, unlike what is observed in the case of asimple electrochemical attack, to maintain an actual physical contactbetween the abrasive particles of the grinding wheel and the workpieceto be shaped, under these conditions only a very limited electrolyteoutput can flow between the two members.

It is the primary object of the present invention to avoid theabove-disclosed inconveniences by permitting the delivery of a largeelectrolyte flow capable of promoting a fast attack of the workpiece tobe shaped while producing between the wheel and the workpiece a contactclose enough to ensure an etficient abrasive action.

Basically, the present invention is characterized by the combination, ina same operation, of successive attacks of the workpiece to be shaped byan electrolytic tool operating under a relatively large electrolyteoutput and with a high current density, so that said tool can operatevery rapidly, with an electrolytic grinding action for grinding thepreviously obtained surface to its final dimensions.

In the drawings:

FIG. 1 is a diagrammatic side-elevational view of a first embodiment ofthis invention, and

FIG. 2 is a similar view showing a modified embodiment.

Referring more in detail to the drawings, FIG. 1 illustrates a workpiece1 connected to the positive terminal of a generator during the shapingof the workpiece by the electrolytic shaping tool 2 and the electrolyticgrinding wheel 3 provided or notwith abrasive elements and bothconnected to the negative terminal of said generator (not shown). Theelectrolytic shaping tool 2 consists-essentially of a massive member ofwhich the lower end portion 8 has a contour complimentary to thesectional shape to be obtained or reproduced along the outer peripheryof workpiece 1. This tool 2 is carried by arms 9 connected to a link 7or to any other suitable and known means permitting of presetting thetool 2 and more particularly adjusting the distance from this tool 2 tothe workpiece 1.

The shaping tool 2 is connected via a conductor 4 to the negativeterminal of the generator. It is supplied with electrolyte by means ofconduits or hoses 5 and 6 controlled separately by valves 10, 10 andleading to the shaping tool proper and also to the grinding wheel 3; itwill be seen that an inner volume is formed between the grinding wheel 3and the rear portion of the tool 2,

to promote the accumulation of electrolyte carried along by the wheelrotation and caused to engage the workpiece 1 at point B, where thegrinding wheel is operative.

During the grinding operation the workpiece 1 and grinding wheel 3 arerotatably driven about their axes O and 0' respectively in oppositedirections, as shown by the arrows, and the tool 2 is moved towards theworkpiece by acting upon the link 7. The current generator has itspositive terminal connected to the workpiece I and its negative terminalconnected to both tool 2 and wheel 3.

Thus, the electrolyte is delivered via the hoses 5 and 6 and when thedistance between the tool 2 and workpiece 1 is reduced sufliciently (butwithout producing an actual contact) the metal is attacked at Aaccording to the shape of the surface 8 of tool 2.

Then, through its rotation, the previously machined surface of workpiece1 is moved to point B at the level of grinding wheel 3 of which thesurface has exactly the dimensions and shape of the desired workpiece 1but in negative form.

The work performed at said point B consists in effecting an accurategrinding operation under a low current density.

As the greater part of the metal to be removed has already beeneliminated (at point A), the wheel 3 removes at B only a few hundredthsof a millimeter of this metal. Therefore, the mechanical stress appliedto this wheel 3 is relatively moderate and the wheel material mayconsist of a light alloy or other light-weight, moderate-strength andrelatively cheap material such as graphite, in contrast withconventional machines requiring the use of stressresisting andconsiderably more expensive materials, such as sintered copper coatedwith diamond particles. The graphite grinding wheel, which is free ofany abrasive substance and does not actually engage the workpiece,operating in this case only by electrolytic action.

The wheel 3 and tool 2 operate simultaneously until the entire outerperiphery of the workpiece 1 has been treated by both means. However,when the rough-shaping tool 2 has completed its peripheral work, it ishacked and disconnected automatically, and the electrolyte flow issuingfrom conduit 5 is cut off by closing the valve 10 to prevent a secondpass which, in the long run, would remove excessive material from theworkpiece 1.

This operation may be programmed or controlled through any known andsuitable means such as a device for detecting the workpiece dimension,for example an electric photocell.

Similarly, these operations are performed immediately after the grindingwheel 3 has completed in turn its peripheral run on workpiece 1.

The modified form of embodiment illustrated in FIG. 2 departs from thepreceding one in that the electrolytic tool 22 is mounted independentlyof the grinding wheel 23.

In this structure the homologues of the component elements alreadydescribed with reference to FIG. 1 are designated and arranged asfollows:

The workpiece 21 receiving a positive charge is attacked by the tool 22and subsequently by the electrolytic wheel 23, both tool and wheel beingcharged negatively and supplied separately and adjustably withelectrolyte at 25 and 26, respectively. The element 29 retained byspring 30 permits moderation of the electrolyte zflow from hose orconduit 26. The tool 22 is adapted to be positioned by means of a knowndevice 27 consisting for example of a handwheel controlling thelongitudinal and transverse movements of said tool.

The operation of this structure is substantially identical with that ofthe structure shown in FIG. 1, and comprises the following steps:

quickly attacking the blank at A with electrolyte,

grinding the workpiece 21 to the final dimensions at B by means of theelectrolytic grinding wheel 23,

automatically retracting the tool 22 and wheel 23, and also theworkpiece 21 upon completion of the peripheral treatment thereof,concomitantly with the cutting off of the current and electrolytesupplies.

The essential differences between the two forms of embodiment may bedescribed as follows:

The shape of the shaping end 28 of tool 22, which operates only througha profile, whereas the homologue end 8 of tool 2 operates throughout itsoblique surface, thus requiring a more sophisticated and therefore moreexpensive tool in the case of FIG. 1.

The direction of rotation in the embodiment of FIG. 2 is such that therotational speeds of the grinding wheel and of the workpiece addthemselves at point B, thus improving the machining performances andefiiciency.

The adjustment of the working position of the electrolytic tool 22 iscompletely independent of that of grinding wheel 23, an advantage notobtained with the arrangement of FIG. 1.

It would not constitute a departure from the basic principle of thepresent invention to modify various details of the device, for examplewith a view to machine workpieces having different shapes, as willreadily occur to those conversant with the art.

What is claimed as new is:

1. A device for electrochemically grinding workpieces by removingmaterial from the surface of conducting work-pieces, comprising: toolmeans for shaping a movable workpiece, a source of electrical currenthaving one pole connected to said tool means and a second pole forconnection to a workpiece; means for supplying an electrolyte fluid tosaid tool means; said tool means comprising a first member for rapidlyelectrolytically attacking a rough-shaped rotating workpiece said firstmember comprising a support forming an electrolytic tool having astationary front end shaped as a complimentary negative of the sectionalcontour to be obtained on a workpiece, and including means for inputtinga high flow of electrolyte fluid and a terminal for a high-densitycurrent supply; and a second member comprising an electrolytic grindingwheel located separate from, but at the rear part of, said support, forgrinding a rough-shaped workpiece after passage of said workpiece nearsaid first member support; and the rear part of said supportadditionally comprising a damming bulk for retaining electrolyte fluid.

2. The device of claim 1, wherein said first member is secured tosupport means which is adjustable for locating said first member.

3. The device of claim 2, including means for rotating said electrolyticgrinding wheel and a workpiece in the same direction of rotation.

4. The device of claim 1, including means for rotating said electrolyticgrinding wheel and a workpiece in opposite directions of rotation.

5. A device for electrochemically forming workpieces, comprising: meansfor removing material from the surface of an electrically conductiveworkpiece, comprising a first tool having a stationary working surfaceshaped as the compliment of the sectional contour desired to be obtainedon a workpiece, with means for supplying electrolyte fluid through saidfirst tool to said working surface, and means for supplying a highdensity current to the working surface of said first tool;

and a second tool comprising an electrolytic rotating grinding wheel andmean for supplying electrolyte fluid to a nip space between the surfaceof said wheel and the path of the surface of a rotating conductiveworkpiece, and means for supplying a current to the surface of saidgrinding wheel;

said second tool being located downstream from said first tool along thepath of the surface of said rotating conductive workpiece;

adjustable support means upon which said first tool is supported foradjusting the position of the working face of said first tool withrespect to the path of the surface of said rotating conductiveworkpiece;

a source of electric current having one pole connected to said tools,and another pole counectable to a conductive workpiece;

5 6 means for controlling the amount of electrolyte fluid 3,476,66211/1969 Inoue 204224 M supplied to said nip space in proportion to thesize 3,410,980 11/ 1968 Gugger et a1. 204129.35 X of said nip space; andmeans for retaining said electrolyte fluid emerging FOREIGN PATENTS fromthe path of the surface of said rotating con- 5 75 22 5 /1959Switzerland 5 ductive workpiece.

References Cited FREDERICK C. EDMUNDSON, Primary Examiner UNITED STATESPATENTS USCL 3,061,529 10/1962 Crompton 204224 M 10 204 129 35 129 41295 Dig 12 3,616,427 10/1971 Linden 204212

